Method of manufacturing a spar for a wind turbine from elements having end portions extending transversely to an intermediate portion

ABSTRACT

The invention provides a method of manufacturing a spar for a wind turbine blade. The method includes providing at least two caps, each cap forming an intermediate portion between two end portions, where the end portions each forms a cap joint surface portion along a longitudinal extending edge of the end portion and the intermediate portion forms an outer surface portion of the spar, providing at least two webs, each web being provided with web joint surface portions along opposite and longitudinally extending edges, and connecting the joint surface portions of the caps with the joint surface portions of the webs to form a tubular configuration of the spar. The caps are provided so that the end portions extend transversely to the intermediate portion and the caps are arranged relative to each other so that the end portions of one cap extend from the intermediate portion towards the end portions of another cap.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a spar for awind turbine and to the spar itself.

BACKGROUND OF THE INVENTION

Traditionally a spar acts as a reinforcing beam in a wind turbine blade.The spar is located between two shell parts, one defining a windwardside shell part and the other one defining a leeward side shell part.The spar is located in the cavity between the two wind turbine shellparts and extends substantially throughout the shell cavity in order toincrease the strength of the wind turbine blade.

In order to increase the strength of the spar and in order to limit theweight hereof, composite materials are often used for spars to be usedin wind turbine blades, since such blades are exposed to varying loadswith high peeks.

Traditionally, a spar is a tubular element being manufactured by the useof a male mould, e.g. by winding a suitable material around a mandrel ora similar core element.

When winding or by other means applying a material onto a mandrel or acore, the inner geometry of the final tubular element is defined by thegeometry of the mandrel or core, thus allowing for a well-defined innergeometry. On the contrary, the outer geometry of the final tubularelement is less well-defined as the effect of even small variations onthe mandrel or core and/or small variation on the innermost layers ofthe winded material are increased with the number of windings.

Alternatively, a spar is sometimes made from two separately mouldedelements which subsequently are joined in order to define a tubularelement. In order to achieve a tubular element of the right size, aheight adjustment element can be applied to assure that the final sparfits in the cavity between the two shell parts defining the wind turbineblade.

SUMMARY OF THE INVENTION

It is an object of embodiments of the present invention to provide animproved method of manufacturing a spar for a wind turbine blade and toprovide an improved spar.

Thus, in a first aspect, the invention provides a method ofmanufacturing a spar for a wind turbine blade, the method comprising thesteps of:

-   -   providing at least two caps, each cap forming an intermediate        portion between two end portions, where the end portions each        forms a cap joint surface portion along a longitudinal extending        edge of the end portion and the intermediate portion forms an        outer surface portion of the spar,    -   providing at least two webs, each web being provided with web        joint surface portions along opposite and longitudinally        extending edges, and    -   connecting the joint surface portions of the caps with the joint        surface portions of the webs to form a tubular configuration of        the spar        wherein the caps are provided so that the end portions extend        transverse to the intermediate portion, and wherein the caps are        arranged relative to each other so that the end portions of one        cap extend from the intermediate portion towards the end        portions of another cap.

The at least four spar parts, the caps and the webs, are connected toform a tubular element which may constitute part of the longitudinalstrength of the wind turbine blade, thus being part of the reinforcementof the blade.

It should be understood, that by tubular element is in this connectionmeant a hollow element with an elongated shape. The shape may benon-uniform. The outer geometry may be of a substantially rectangularshape, a partly circular shape, an oval shape or any other shape. Theinner geometry may be different from the outer shape, thus defining atubular element in the form of an elongated ring of an arbitrary shape.

In a cross section the spar may be substantially rectangular, e.g. withrounded corners. The area of the cross section may decrease from theroot end to the tip end along the length of the spar to have a sparwhich fits a wind turbine blade having a decreased size at the tip endcompared to the root end. However, the width of the spar may increaselocally to increase strength and stiffness of the spar locally. In apreferred embodiment, the spar may thus be approximately conical, i.e.may have a base which is substantially circular transforming into anapproximately rectangular shape with rounded corners and with sideswhich taper towards each other.

As an example, the spar may have a length of approximately 45 meters, amaximum width of approximately 1.0 meters, and a maximum height ofapproximately 0.8 meters. Compared hereto the minimal width of the sparmay be approximately 100 millimeters. It should be understood that thisis only one example of a spar. Other spars being both smaller and largermay also be used depending of the wind turbine blade to be manufactured.

The at least two spar caps may form an upper and a lower part of a sparbeing substantially rectangular, whereas the webs may form substantiallyvertical connections here between when connected at the joint surfaceportions. Thereby providing a spar of at least four separate elements,which may be connected to form a spar with a well-defined outer geometryensuring a better match between the blade shells and the spar.

The caps are provided so that the end portions extend transverse to theintermediate portion. In one embodiment, the end portions extend fromthe intermediate portion at an angle of 75-100 degrees, such asapproximately 90 degrees, thus forming a cap being U-shaped along thelength of the assembled spar.

Caps having end portions extending transverse to the intermediateportion may ensure a good bond between the end portions of the caps andthe webs. Furthermore, this configuration may facilitate distribution ofthe shear forces, as the bond between the cap and the web will be loadedin shear.

A bend portion may connect the intermediate portion and each of the endportions. In the bend portion, the caps may have a larger curvature sothat each of the end portions extends transverse to the intermediateportion with an angle being within a predefined range, such as a rangeof 75-100 degrees.

The method comprises a step of arranging the caps relative to each otherso that the end portions of one cap extend from the intermediate portiontowards the end portions of another cap. Thereby, the web joint surfaceportions may be connected to the cap joint surface portions by arrangingthe webs so that they extend between the end portions of the caps withthe web joint surface portions overlapping the cap joint surfaceportions, thus forming a spar being tubular.

The caps may be arranged relative to each other so that a predefineddistance is formed between the outer surface portions of the caps priorto the step of connecting the joint surface portions of the caps withthe joint surface portions of the webs. This allows for assembling of aspar having a well-defined height, and thus a spar matching the size andshape of the blade shells more precisely.

The webs may be provided as substantially flat panels to facilitateconnection of the joint surface portions of the caps and webs. This mayespecially be an advantage if the caps are arranged relative to eachother so that the end portions of one cap extend from the intermediateportion towards the end portions of another cap.

The caps may be provided so that an angle existing between the endportions and the intermediate portion may vary under elastic deformationof the caps. The angle may be an angle above 90 degrees. As the jointsurface portions of the webs may be connected to the cap joint surfaceportions by arranging the webs so that they extend between the endportions of the caps with the web joint surface portions overlapping thecap joint surface portions, the webs may be pressed towards the capsduring assembling of the spar. When pressing the webs towards the caps,the caps may be deformed, as the end portions of each of the caps may bepressed towards each other whereby the angle may change towards an angleof approximately 90 degrees.

In one embodiment, at least one of the caps is moulded in a cap mould,whereby the joint surface portions of the cap are shaped by contact withthe cap mould during moulding thereof. By shaping the cap joint surfaceportions by contact with the mould, these portions can be especiallywell designed for connection with the joint surfaces of the webs, as thecap joint surfaces portions may have a surface structure being optimizedfor e.g. an appropriate adhesive and/or a shape which accurately matchesa corresponding web joint surface.

The caps may form an outer surface of the tubular spar, which outersurface is geometrically defined by contact with the cap mould duringmoulding thereof. Consequently, not only the cap joint surfaces may bedefined by contact with the mould, also the outer surface of theintermediate portion may be defined by the mould.

Furthermore, each web may be moulded in a web mould, and the jointsurface portions of the webs may be geometrically defined by contactwith the web mould during moulding thereof. Alternatively, the webs maybe substantially plain sheets of a non-moulded material, such as plasticor wood.

If moulded, the webs may form an inner surface of the tubular spar,which inner surface is geometrically defined by contact with the webmould during moulding thereof.

The caps and webs may be provided so that they comprise differentmaterials. As an example, both the caps and the webs may comprise fibrereinforced plastic, where the fibres of the caps may mainly be carbonfibres and the fibres of the webs may mainly be glass. The resin may bethe same for both, or may be different forms of resin. Other materialsmay also be used, either as an alternative to or in combination with thefibre reinforced plastic.

Furthermore, the intermediate portions and the end portions may beprovided so that they comprise different materials. In one embodiment,the intermediate portion mainly comprises carbon fibre reinforcedplastic, whereas the end portions mainly comprises glass fibrereinforced plastic.

The most commonly used materials for the intermediate portion may beunidirectional fibres and a resin matrix. A filler may also be added.The fibres may e.g. be carbon, glass, wood or natural fibres. As anexample, the resin may be a thermoset resin, such as Epoxy, or it may bea thermoplastic resin, such as PET (Polyethylene Terephtalate). Anexample of a suitable filler is Nano particles.

The most commonly used material for the end portions may be biaxiallyfibres and a resin matrix. The fibre may e.g. be of glass or wood. Andas an example, the resin may be a thermoset resin, such as Epoxy, or itmay be a thermoplastic resin, such as PET.

The materials may be selected so that the intermediate portions and theend portions have different characteristics with respect to strength.Thereby it may be obtained that the intermediate portions and the endportions have different ability to support a load, and/or have differentlevels of stress at which there is a significant change in the state ofthe material, stress being at least one of tensile stress, compressivestress, or shear stress.

Furthermore, the materials may be selected so that the intermediateportions and the end portions have different characteristics withrespect to flexibility. Thereby the intermediate portions and the endportions may have different property of being flexible, i.e. differentlevel of how easily they are bent or shaped. In other words, thematerials may be different in relation to the extent to which and therate at which adjustments to changed circumstances are possible.

A transition zone may be provided between the intermediate portion andthe end portions. This transition zone may be provided with a graduallychanged composition of the different materials which the intermediateportion and the end portion comprise. Thus, in the transition zone theresin may change gradually, the fibres may change gradually, or both maychange gradually. Other materials of the intermediate portion and theend portion may also change gradually.

The webs may be provided as sandwich constructions having a corecomprising e.g. a thermoplastic or thermoset foam or balsa. Other corematerials may also be used. The webs may comprise an inner and an outerlayer on each side of the core, which layers as an example may primarilycomprise biaxially fibres and a resin matrix. The fibres may e.g. beglass fibres and the resin may e.g. be a thermoset resin, such as Epoxy,or it may be a thermoplastic resin, such as PET.

The caps and webs may be provided with different structures, e.g. eitherdue to the use of different materials or due to the use ofunidirectional and biaxially fibres, respectively.

The webs and caps may be provided as laminated elements by moulding ofat least one type of fibre material and at least one type of resin inindividual moulds. Each of the caps may be moulded as a single piece toavoid assembling of the caps of a plurality of cap elements. However,assembling of cap elements may be a step in one embodiment of themethod.

As the windward side shell and the leeward side shell of the turbineblade may curve slightly differently, the at least two individual mouldsfor the caps may be differently shaped.

Likewise, individual moulds may be used to provide the webs. The webs inone embodiment may be provided of a plurality of web elements, each webelement being moulded in a separate mould. As an example, each web maycomprise a plurality of web element with a length in the range of 5-15meters, such as 10 meters per element. The web elements may be ofdifferent length. It should be understood, that a web may alternativelycomprise a number of substantially plain web elements of a non-mouldedmaterial.

Consequently, the method may further comprise a step of assembling thewebs from a plurality of web elements. The webs may be assembled fromthe web elements before connecting the caps and webs to form the spar,or alternatively, the web elements may be connected while simultaneouslyconnecting the caps and web and thus forming the spar.

The web joints, i.e. joints between two adjacent web elements, may bestaggered along the length of the assembled spar to avoid that webjoints on opposite sides of the spar are positioned vis-à-vis eachother.

To form a spar by connecting the caps and webs, the method may furthercomprise a step of applying an adhesive to at least one of the jointsurface portions and a step of curing the adhesive. The adhesive may becured by use of heating.

To be able to position the caps and webs relative to each other beforeconnecting them, it may be an advantage if the caps and webs comprise anassembly marking, as such a marking may facilitate positioning of thecaps and webs relative to each other. The markings may be providedduring moulding of the caps and webs, as the moulds as an example maycomprise one or more datums, e.g. in the form of small protrusionsforming an indentation in the caps and webs during moulding hereof.

To facilitate connection of the spars and the webs, the method mayfurther comprise a step of providing an assembly tool, and a step ofarranging the caps and webs herein prior to the step of connecting thecaps and webs.

The assembly tool may comprise a support and consequently, the step ofarranging the caps and webs in the assembly tool may comprise a step ofarranging them in this support so that the caps and webs are positionedin a specific position relative to each other, thereby facilitatingcorrect positioning of the spars and webs before connecting them.

When positioning the spar between two shell parts of a wind turbineblade, the outer surface portion may form a contact face for assemblywith a blade shell. The spar may be attached to the shell part by addingan adhesive to the outer surface portion of each of the caps andsubsequently position the shell parts around the spar so that a part ofan inner surface of the each of the shell parts is attached to the outersurface portion of each of the caps.

In an alternative embodiment, the outer surface portion may be adaptedto form part of an aerodynamically active surface of a wind turbineblade. Thus, the spar may not be completely encapsulated within theshell parts.

The spar may comprise more elements than the caps and webs. In oneembodiment, the spar further comprises a separate root section. Thus,the method may further comprise a step of attaching the root sectionwhich is formed as a separate section to the caps and webs. The rootsection may be attached during connection of the joint surfaces of thecaps and webs, or it may be attached subsequently. The root section maybe attached by different processes, such as by bonding, wrapping, orinfusion.

The method may further comprise a step of providing in a root end of thespar, a plurality of attachments structures facilitating attachment ofthe blade to a hub. The root end may form part of a separate rootsection or it may form part of a spar being assembled from caps and webswithout a separate root section. An attachment structure may as anexample comprise a hollow steel member with an internal threading intowhich a bolt or another threaded member may be fixed.

To facilitate lightning protection of the wind turbine blade, the methodmay further comprise a step of providing a short circuit in each of thecaps. The short circuits may connect the caps electrically. The shortcircuit may as an example be thin copper plates which are connected toeach other and to a down conductor. The short circuits may be laminatedinto the caps.

To increase the stability of the spar, the method may further comprise astep of attaching a stiffening element to at least one of the caps, thestiffening element being arranged to increase a stiffness of the spar inthe longitudinal direction. The stiffening element may be attached e.g.during moulding of the caps or during assembling of the spar whenconnecting the joint surface portions of the caps and webs.

Examples of stiffening elements are a transverse member being attachedto and extending from an inner surface of one cap to the inner surfaceof another cap, and different elongated members being attached to aninner surface of the caps and extending along the caps. Another exampleof a stiffening element is a rib member comprising of a plurality ofribs being attached to an inner surface of the caps. The ribs can bepositioned adjacent to each other with a mutual distance of e.g. 1meter. Other stiffening members may also be used.

In a second aspect, the invention provides a spar for a wind turbineblade, the spar having a tubular structure and being assembled from atleast two caps and two webs, the caps each forming an intermediateportion between two end portions, where the end portions each forms acap joint surface portion along a longitudinal extending edge of the endportion and the intermediate portion forms an outer surface portion ofthe spar, and the webs each having web joint surface portions alongopposite and longitudinally extending edges, where the joint surfaceportions of the caps are connected to the joint surface portions of thewebs, where the end portions extend transversely to the intermediateportion, and where the end portions of one cap extend from theintermediate portion towards the end portions of another cap.

The spar may be manufactured by use of the method of the first aspect ofthe invention. It should be understood, that the features of theabove-mentioned first aspect of the invention may also be applicable tothe spar of the second aspect of the invention.

In particular the spar may comprise:

-   -   caps arranged relative to each other with a predefined distance        formed between the outer surface portions of the caps before the        joint surface portions of the caps are connected with the joint        surface portions of the webs,    -   webs comprising substantially flat panels,    -   caps having an angle between the end portions and the        intermediate portion, which may vary under elastic deformation        of the caps,    -   joint surface portions of the caps being shaped by contact with        a cap mould,    -   intermediate portions and end portions comprising different        materials,    -   webs comprising a plurality of web elements,    -   a short circuit in each of the caps, the short circuits        connecting the caps electrically to facilitate lightning        protection of the blade, and/or    -   a stiffening element attached to at least one of the caps, the        stiffening element being arranged to increase a stiffness of the        spar in the longitudinal direction.

In a third aspect, the invention provides a spar for a wind turbineblade, the spar having a tubular structure and being assembled from atleast two caps and two webs, the caps each forming an intermediateportion between two end portions, where the end portions each forms acap joint surface portion along a longitudinal extending edge of the endportion and the intermediate portion forms an outer surface portion ofthe spar, and the webs each having web joint surface portions alongopposite and longitudinally extending edges, where the joint surfaceportions of the caps are connected to the joint surface portions of thewebs, wherein at least one of the webs comprises at least two adjacentweb elements with interfaces not being connected to each other.

This means, that these adjacent web element are not directly connectedto each other but only connected to each other via the caps to whichthey are both joined. Consequently, they are not bonded, glued, screwedor similarly attached to each other.

The spar may be manufactured by use of the method of the first aspect ofthe invention. It should be understood, that the features of theabove-mentioned first and second aspects of the invention may also beapplicable to the spar of the third aspect of the invention.

In a fourth aspect, the invention provides a blade for a wind turbinecomprising a spar according to the second or third aspect of theinvention. The spar may be manufactured according to the first aspect ofthe invention. It should be understood, that the features of the first,second, and third aspects previously described may also be applicable tothe fourth aspect of the invention.

When connecting the joint surface portions of the caps and webs to forma spar, an assembly tool may be used. An example of such an assemblytool could be:

An assembly tool for assembling a spar for a wind turbine blade, thespar comprising at least two caps and two webs, each cap forming anintermediate portion between two end portions, where the end portionseach forms a cap joint surface portion along a longitudinal edge of theend portion and the intermediate portion forms an outer surface portionof the spar, and each web having web joint surface portions alongopposite and longitudinally extending edges, the tool comprising a capsupport for holding caps, a web support for holding webs and an assemblystructure facilitating positioning of the supports relative to eachother.

By positioning the caps and webs relative to each other it may befurther be ensured that the geometry of the spar is more preciselyadapted to the geometry of the final turbine blade.

The assembly structure may comprise a hinge structure facilitatingrotation of one support relative to an adjacent support. Thus, thesupports may be connected to each other by a hinge structure which uponrotation of one support relative to an adjacent support facilitatespositioning of the supports relative to each other.

In an initial open configuration, in which the assembly tool may beready to receive the caps and webs, the supports may all be positionedwith an upper support surface facing upwards. After having positionedthe caps and webs in the supports, the assembly structure may facilitatethat three of the four support structures are lifted and rotatedrelative to each other and relative to the last support structure whichmay stay in its initial position having the upper support surface facingupwards. The lifting and rotational movement may be controlled andlimited by the hinge structure of the assembly structure whichfacilitates correct rotation of the supports relative to each other.

As an alternative to the hinge structure, the assembly structure maycomprise an attachment structure facilitating attachment of at least onesupport to at least another support. The supports may still in aninitial position be positioned with the upper support surface facingupwards. And after having positioned the caps and webs in the supports,each of the supports may be moved to the correct position where theattachment structure may ensure that a support is attached to at leastone of the adjacent supports to form a tubular spar.

To facilitate positioning of the supports relative to each other, theassembly structure may comprise a power driven element for positioningthe supports relative to each other. The power driven element maycomprise a hydraulic structure, an electrical structure, a crane device,or other power structures.

At least one of the supports may comprise a tool marking which matches acorresponding assembly marking on at least a cap or a web. Thesemarkings may facilitate positioning of the cap or web relative to thesupport, thereby ensuring a correct final position of caps and websrelative to each other before connecting them.

In one embodiment, the tool marking comprises one or more protrusionsand the corresponding assembly marking comprises one or moreindentations. These protrusions are arranged for engagement with theindentations of the cap or web. In an alternative embodiment, theassembly marking comprises one or more protrusions, whereas the toolmarking comprises one or more indentations. Other corresponding markingsfacilitating positioning of the caps or web relative to the assemblytool may be used in other embodiments.

To ensure that a cap or web stays within a support structure as long asnecessary, the supports may comprise a fixing structure facilitatingfixing of a cap or a web to each of the supports. A fixing structure maybe provided for each of the support structures. The cap and/or web maybe fixed e.g. by magnetic forces, by the use of suction pressure, bybonding, by screws, rivets, or by other means.

As the manufactured caps and/or webs may have a degree of longitudinalbending due to thermal shrinkages, it may be an advantage if theassembly tool further comprises a manipulation structure adapted tomanipulate part curvature and twist of at least one of the caps andwebs. Thereby, the required tolerances may be met. By part curvature isin this connection understood the longitudinal bending of at least apart of the caps and/or webs. Furthermore, twist should be understood tocover a partly rotation of a part of the caps and/or webs.

The assembly tool may further comprise a heating structure facilitatingcuring of an adhesive provided at least one of the joint surfaceportions. As an example, the heating structure may comprise electricallyheated wires being built-in the supports at positions at which the jointsurface portions are positioned during assembling of the spar.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be further described withreference to the drawings, in which:

FIG. 1 a is illustrates an embodiment of a spar having a tubularstructure and being assembled from at least two caps and two webs,

FIG. 1 b is an enlarged view of FIG. 1 a is illustrating a joint betweena cap and a web,

FIGS. 2 a and 2 b illustrate different embodiments of a spar comprisinga plurality of web elements,

FIG. 2 c is an enlarged view of a part of FIG. 2 b,

FIG. 2 d illustrates an embodiment of a spar comprising a plurality ofweb elements,

FIG. 3 a illustrates a spar mould for a cap,

FIG. 3 b illustrates a web mould for a web,

FIGS. 4 a and 4 b illustrate two different ways of attaching the spar towind turbine blade shells,

FIG. 5 illustrates a spar comprising intermediate portions and endportions of different materials, and webs comprising sandwichconstructions,

FIGS. 6 a-6 d illustrate different embodiments of a spar comprisingdifferent stiffening elements,

FIGS. 7 a and 7 b illustrate different embodiments of a spar withdifferent root ends,

FIGS. 8 a and 8 b illustrate a spar comprising a lightning protectionfor a wind turbine blade, and

FIGS. 9 a and 9 b illustrate an assembly tool for a spar.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 a illustrates an embodiment of a spar 1 for a wind turbine blade(not shown). The spar 1 comprises two caps 2 a, 2 b and two webs 3 a, 3b.

Each cap 2 a, 2 b forms an intermediate portion 4 between two endportions 5. The end portions 5 each forms a cap joint surface portion 6and the intermediate portion 4 forms an outer surface portion 7.

Each web 3 a, 3 b is provided with web joint surface portions 8 alongopposite and longitudinally extending edges.

When connecting the joint surface portions of the caps 6 with the jointsurface portions of the webs 8, a spar 1 having a tubular configurationis formed. An adhesive 9 is used to bond the joint surface portions 6, 8together as illustrated in FIG. 1 b which shows an enlarged part of FIG.1 a.

The caps 2 a, 2 b and webs 3 a, 3 b are moulded in cap moulds and webmoulds, and their joint surface portions 6, 8 are geometrically definedby a shape of these moulds. I.e. the joint surface portion 6, 8 areshaped by contact with the mould ensuring a well-defined geometry of thejoint surface portions 6, 8.

As illustrated, the end portions 5 of the caps 2 a, 2 b extendtransversely to the intermediate portion 4 at an angle of approximately90 degrees, whereby the end portions 5 of the one cap 2 a extend fromthe intermediate portion 4 towards the end portions 5 of the other cap 2b when the spar 1 is assembled. The webs 3 a, 3 b are attached to thecaps 2 a, 2 b at the end portions 5.

FIG. 2 a illustrates parts of an embodiment of a spar 1 in which thewebs 3 a, 3 b comprise a plurality of web element 10 a, 10 b. To avoid abutt joint between the web elements 10 a, 10 b, each of the web elements10 a, 10 b comprises a joint surface 11 a, 11 b ending at an acuteangle. This increases the area of the joint surfaces 11 a, 11 b andfacilitates joining of the web elements 10 a, 10 b.

FIGS. 2 b and 2 c illustrate an alternative embodiment of a spar 1 inwhich the webs 3 a, 3 b comprise a plurality of web element 10 a, 10 b,10 c. Instead of the overlap joint illustrated in FIG. 2 a, the webelements 10 a, 10 b are joined at their end sections forming, in thisembodiment, an elliptical cut-out leaving a hole 36 in the webs 3 a, 3b. In the cut-out area 36, the shear loads are taken by the caps 2 a, 2b.

FIG. 2 b further illustrates that the web joints, i.e. the jointsbetween two adjacent web elements 10 a, 10 b, and 10 b, 10 c arestaggered along the length of the assembled spar 1 to avoid that webjoints on opposite sides of the spar 1 are positioned vis-à-vis eachother. This way of staggering the web joints is also applicable for theweb joints of FIG. 2 a.

FIG. 2 d illustrates a further alternative of an embodiment of a spar 1in which the webs 3 a, 3 b comprise a plurality of web element 10 a, 10b, 10 c. As illustrated, two adjacent web elements 10 a, 10 b-10 b, 10 chave interfaces 100 which are not connected to each other.

This means, that these adjacent web elements 10 a, 10 b-10 b, 10 c arenot directly connected to each other but only connected to each othervia the caps 2 a, 2 b to which they are both joined. Consequently, theadjacent web elements 10 a, 10 b-10 b, 10 c are not bonded, glued,screwed or similarly attached to each other.

When not connecting the web elements 10 a, 10 b-10 b, 10 c only bondingof the caps 2 a, 2 b and webs 3 a, 3 b is needed and extra bonding forthe web elements can be omitted. This may both decrease the amount ofadhesive needed when assembling the spar 1 and the time involved inassembling the spar, and thus lower the costs associated herewith. Theholes 36 can be used for inspection access and are shaped so that theyminimize stress concentrations on the end of the web elements.

FIG. 3 a illustrates an embodiment of a cap mould 12 with a cap 2 a, andFIG. 3 b illustrates an embodiment of a web mould 13 with a web 3 a.

The cap mould 12 comprises a lower mould 14 and two upper mouldextensions 15. The inner surface of the upper mould extensions 15 isprovided with a material which does not adhere to the resin of the cap 2a and which furthermore is able to geometrically define the cap surfacejoint portions 6 by contact herewith. An example of such a material ispeal ply.

The outer surface portion 7 of the intermediate portion 4 is alsodefined by contact with the inner surface of the cap mould 12.

The inner surface of the cap mould 12 comprises two datums 16 in theform of small protrusions, a little cone. The datums 16 each forms anindentation 17 in the cap 2 a during moulding hereof. These indentations17 are used to position the cap 2 a relative to the webs 3 a, 3 b (notshown) before connecting them. The positioning can be done by use of anassembly tool.

As illustrated in FIG. 3 b, the inner surface 18 and the web jointsurface portions 8 of the web 3 a are defined by contact with the webmould 13, thus allowing for a well-define geometry of the web jointsurface portions 8 which are to be joined with the cap surface portions5. I.e. the matching joint surfaces portions 6, 8 are moulded tofacilitate a more precise joint between the caps 2 a, 2 b and webs 3 a,3 b.

FIGS. 4 a and 4 b illustrate two different ways of attaching the spar 1to the shells of a wind turbine blade 19.

In FIG. 4 a the spar 1 is positioned between two blade shells 20 a, 20 bof the wind turbine blade 19 a. Blade shell 20 a corresponds to asuction side of the turbine blade 19 a and blade shell 20 b correspondsto a pressure side of the turbine blade 19 a. The outer surface portions7 form a contact face for assembly with the blade shells 20 a, 20 b. Thespar 1 is attached to the blade shells 20 a, 20 b by adding an adhesive(not shown) to the outer surface portion 7 of each of the caps 2 a, 2 b.As shown in FIG. 4 a, the spar 1 is oriented such that the cap 2 aconfronts the suction side of the turbine blade 19 a and the cap 2 bconfronts the pressure side of the turbine blade 19 a.

In FIG. 4 b an alternative embodiment is illustrated. The outer surfaceportions 7 are adapted to form part of the aerodynamically activesurface of the wind turbine blade 19 b. Thus, the spar 1 is notcompletely encapsulated within the blade shells 21 a, 21 b, 21 c. Bladeshell 21 a corresponds to a suction side of the turbine blade 19 b andblade shell 21 b corresponds to a pressure side of the turbine blade 19b. As shown in FIG. 4 b, the spar 1 is oriented such that the cap 2 aforms part of the suction side of the turbine blade 19 b and the cap 2 bforms part of the pressure side of the turbine blade 19 b.

FIG. 5 illustrates a spar 1 comprising two caps 2 a, 2 b and two webs 3a, 3 b. The caps 2 a, 2 b comprise intermediate portions 4 and endportions 5 of different materials. And the webs 3 a, 3 b are provided assandwich constructions.

In the illustrated embodiment, the intermediate portions 4 compriseunidirectional fibres, a resin matrix, and a filler. The main part ofthe fibres is carbon fibres. The end portions 5 comprise biaxiallyfibres and a resin matrix. The main part of the fibres is glass fibres.

The webs 3 a, 3 b are provided as sandwich constructions having a core22 comprising a foam. The webs 3 a, 3 b further comprise an outer 23 andan inner layer 24 on each side of the core 22. These layers 23, 24primarily comprise biaxially fibres, in the form of glass fibres, and aresin matrix.

FIGS. 6 a-6 d illustrate different embodiments of a spar 1 comprisingdifferent forms of stiffening elements 25 to increase the stability ofthe spar 1. The stiffening element 25 is attached to at least one of thecaps 2 a, 2 b.

FIG. 6 a illustrates a stiffening element 25 a in the form of atransverse member being attached to and extending from the inner surfaceof the upper cap 2 a to the inner surface of the lower cap 2 b.

FIG. 6 b illustrates a stiffening element 25 b in the form of twoelongated members each being attached to the inner surface of one of thecaps 2 a, 2 b and extending along the caps 2 a, 2 b. The stiffeningelement 25 b is formed as a T-beam.

FIG. 6 c illustrates a stiffening element 25 c in the form of twoelongated members each being attached to the inner surface of one of thecaps 2 a, 2 b and extending along the caps 2 a, 2 b. The stiffeningelement 25 b is formed as an Omega shaped beam.

FIG. 6 d illustrates a stiffening element 25 d in the form of a ribmember comprising of a plurality of ribs. The ribs are attached to theinner surface of the caps 2 a, 2 b and positioned adjacent to each otherwith a mutual distance of approximately 1 meter.

FIGS. 7 a and 7 b illustrate different embodiments of a spar 1 havingdifferent root ends 26.

FIG. 7 a illustrates an embodiment of a spar comprising a separate rootsection 27. The root section 27 has been attached by bonding, wrapping,or infusion.

A plurality of attachments structures 28 facilitating attachment of theblade (not shown) to a hub (not shown) are provided in the root end 26of the spar 1. In FIG. 7 a, the attachment structures 28 are provided inthe root end 26 of the separate root section 27, whereas FIG. 7 billustrates a spar 1, in which the attachment structures 28 are providedin the caps and webs. The attachment structures 28 are hollow steelmembers with an internal threading into which a bolt or another threadedmember from the hub can be fixed.

FIGS. 8 a and 8 b illustrate a spar 1 comprising a lightning protectionfor a wind turbine blade. FIG. 8 b is an enlarged view of a part of FIG.8 a.

Lightning protection is provided by laminating a short circuit 29 intoeach of the caps 2 a, 2 b. The short circuits 29 connect the caps 2 a, 2b electrically. The short circuits 29 are thin copper plates which areconnected to each other along one side of the spar 1 in a connection 30.Furthermore, the short circuits 29 are connected to a down conductor 31.

FIGS. 9 a and 9 b illustrate an embodiment of an assembly tool 32 forassembling caps 2 and webs 3 of a spar 1.

The assembly tool 32 comprises a cap support structure 33 for holdingeach cap 2 and web support structure 34 for holding each web 3 duringassembling of the spar 1.

Furthermore, the assembly tool 32 comprises an assembly structurecomprises a hinge structure 35 facilitating rotation of one support 33,34 relative to an adjacent support 33, 34.

FIG. 9 a illustrates an initial open configuration of the assembly tool32, in which the assembly tool 1 has received the caps 2 and webs 3.After having positioned the caps 2 and webs 3 in the supports 33, 34,the assembly structure facilitates that three 33 a, 34 a, 34 b of thefour support structures are lifted and rotated relative to each otherand relative to the last support structure 33 b which stays in itsinitial position having the upper support surface facing upwards. Thelifting and rotational movement is controlled and limited by the hingestructure 35 of the assembly structure which facilitates correctrotation of the supports 33, 34 relative to each other.

FIG. 9 b illustrates a final closed configuration of the assembly tool32, in which the spar 1 is being assembled by connecting the jointsurface portions of the caps 6 with the joint surface portions of thewebs 8. The joint surface portions of the webs 8 are pressed towards thejoint surface portions of the caps 6 by the support structures 34.

Details of the overlap between the joint surface portions of the caps 6and the joint surface portions of the webs 8 can be seen in FIG. 1 b.

The invention claimed is:
 1. A method of manufacturing a wind turbineblade having a suction side and a pressure side and a spar disposedbetween the suction side and the pressure side, the method comprising:prior to assembly, providing at least two caps, each cap forming anintermediate portion between two end portions, where the end portionsextend transverse to the intermediate portion and form a cap jointsurface portion along a longitudinal extending edge of the end portionand the intermediate portion forms an outer surface portion of the spar,prior to assembly, providing at least two webs, each web being providedwith web joint surface portions along opposite and longitudinallyextending edges, assembling the spar by arranging the caps relative toeach other so that the end portions of one cap extend from theintermediate portion towards the end portion of another cap; connectingthe joint surface portions of the caps with the joint surface portionsof the webs to form a tubular configuration of the spar; and orientingthe spar relative to the wind turbine blade such that the intermediateportion of at least one cap confronts or forms part of the suction sideof the wind turbine blade.
 2. The method according to claim 1, whereinthe caps are arranged relative to each other so that a predefineddistance is formed between the outer surface portions of the caps priorto the step of connecting the joint surface portions of the caps withthe joint surface portions of the webs.
 3. The method according to claim1, wherein the webs are provided as substantially flat panels.
 4. Themethod according to claim 1, wherein the caps are provided so that anangle between the end portions and the intermediate portion may varyunder elastic deformation of the caps.
 5. The method according to claim1, wherein the intermediate portions and the end portions are providedso that they comprise different materials.
 6. The method according toclaim 1, wherein the webs and caps are provided as laminated elements bymoulding of at least one type of fibre material and at least one type ofresin in individual moulds.
 7. The method according to claim 1, furthercomprising a step of applying an adhesive to at least one of the jointsurface portions and a step of curing said adhesive.
 8. The methodaccording to claim 1, wherein the caps and webs comprise an assemblymarking facilitating positioning of the caps and webs relative to eachother.
 9. The method according to claim 1, further comprising a step ofproviding an assembly tool, and a step of arranging the caps and websherein prior to the step of connecting the caps and webs.
 10. The methodaccording to claim 1, further comprising a step of assembling the websfrom a plurality of web elements.
 11. The method according to claim 1,further comprising a step of providing a short circuit in each of thecaps, the short circuits connecting the caps electrically to facilitatelightning protection of the blade.
 12. The method according to claim 1,further comprising a step of attaching a stiffening element to at leastone of the caps, the stiffening element being arranged to increase astiffness of the spar in the longitudinal direction.
 13. A wind turbineblade having a suction side and a pressure side and a spar disposedbetween the suction side and the pressure side, the spar having atubular structure and being assembled from at least two caps and twowebs, the caps each forming an intermediate portion between two endportions, where the end portions extend transverse to the intermediateportion and form a cap joint surface portion along a longitudinalextending edge of the end portion and the intermediate portion forms anouter surface portion of the spar, and the webs each having web jointsurface portions along opposite and longitudinally extending edges,where the joint surface portions of the caps are connected to the jointsurface portions of the webs at locations spaced from the intermediateportions of the caps, where the end portions of one cap extend from theintermediate portion towards the end portions of another cap, and wherethe spar is oriented relative to the wind turbine blade such that theintermediate portion of at least one cap confronts or forms part of thesuction side of the wind turbine blade.
 14. The wind turbine bladeaccording to claim 13, wherein the caps are arranged relative to eachother with a predefined distance formed between the outer surfaceportions of the caps before the joint surface portions of the caps areconnected with the joint surface portions of the webs.
 15. The windturbine blade according to claim 13, wherein the webs comprisesubstantially flat panels.
 16. The wind turbine blade according to claim13, wherein an angle between the end portions and the intermediateportion may vary under elastic deformation of the caps.
 17. The windturbine blade according to claim 13, wherein the intermediate portionsand the end portions comprise different materials.
 18. The wind turbineblade according to claim 13, wherein at least one of the webs comprisesa plurality of web elements.
 19. The wind turbine blade according toclaim 13, further comprising a short circuit in each of the caps, theshort circuits connecting the caps electrically to facilitate lightningprotection of the blade.
 20. The wind turbine blade according to claim13, further comprising a stiffening element attached to at least one ofthe caps, the stiffening element being arranged to increase a stiffnessof the spar in the longitudinal direction.
 21. The wind turbine bladeaccording to claim 13, wherein the end portions of one cap are innon-overlapping relationship to the end portions of another cap.
 22. Thewind turbine blade according to claim 13, wherein the end portions ofone cap are coupled to the end portions of another cap only through aweb.
 23. A spar for a wind turbine blade, the spar having a tubularstructure and being assembled from at least two caps and two webs, thecaps each forming an intermediate portion between two end portions,where the end portions each forms a cap joint surface portion along alongitudinal extending edge of the end portion and the intermediateportion forms an outer surface portion of the spar, and the webs eachhaving web joint surface portions along opposite and longitudinallyextending edges, where the joint surface portions of the caps areconnected to the joint surface portions of the webs at locations spacedfrom the intermediate portions of the caps, wherein at least one of thewebs comprises at least two adjacent web elements with interfaces notbeing connected to each other, and wherein the caps extend continuouslybetween the at least two adjacent web elements.
 24. A blade for a windturbine comprising a spar according to claim
 23. 25. The spar accordingto claim 23, wherein the end portions of one cap are in non-overlappingrelationship to the end portions of another cap.
 26. The spar accordingto claim 23, wherein the end portions of one cap are coupled to the endportions of another cap only through a web.